Jet streams are fast, narrow currents of air that flow near the tropopause, roughly 30,000 feet up, circling the globe from west to east. Each hemisphere has a polar jet stream, typically moving around 110 miles per hour with occasional much faster bursts, and a weaker subtropical jet stream closer to the equator at a somewhat higher altitude. They form from the combination of solar heating, which drives large-scale atmospheric circulation, and the Coriolis force, which deflects moving air; the sharper the temperature contrast between neighboring air masses, the stronger the resulting jet. Jet streams typically meander in a wavering path that itself propagates eastward, steering storm systems at lower altitudes and shaping the distribution of precipitation, the development of hurricanes, and seasonal weather patterns, including the shifts in North American rainfall associated with El Nino and La Nina; meteorologists track jet stream position as a key aid to forecasting.
Facts
PeriodicityA persistent feature that 'follows the sun': the northern polar jet stream slowly migrates northward as the Northern Hemisphere warms and southward again as it cools. 1 ScaleThe polar jet typically sits around 9.1 kilometers (30,000 feet) above sea level and travels at roughly 180 km/h (110 mph), though often faster; a jet stream is usually a few hundred kilometers wide with a vertical thickness of less than five kilometers. 1 First DescribedThe first indications of the phenomenon came from the American professor Elias Loomis, who proposed a powerful upper-air current blowing west to east across the United States to explain the behavior of major storms; after the 1883 Krakatoa eruption, weather watchers tracked and mapped the effect on the sky for several years, labeling it the 'equatorial smoke stream'. 1 Identification
Distinguishing AppearanceNot directly visible; its presence is traced by the meandering, wave-like path of upper-level winds, whose large bends are called Rossby waves and which can split into branches or curl into eddies. 1 Sources
1. Jet Stream (Wikipedia)
WikipediaWikipedia 'Jet stream', Description section
The path of the jet typically has a meandering shape, and these meanders themselves propagate eastward, at lower speeds than that of the actual wind within the flow.
Wikipedia 'Jet stream', lead and Description sections
The width of a jet stream is typically a few hundred kilometres or miles and its vertical thickness often less than five kilometres (16,000 feet).
Wikipedia 'Jet stream', Discovery section
The first indications of this phenomenon came from American professor Elias Loomis (1811-1889), when he proposed the hypothesis of a powerful air current in the upper air blowing west to east across the United States as an explanation for the behaviour of major storms.
Wikipedia 'Jet stream', Description section (periodicity sentence)
The northern polar jet stream is said to "follow the sun" as it slowly migrates northward as that hemisphere warms, and southward again as it cools.
Wikipedia 'Jet stream', Description section (distinguishing-appearance sentence)
The path of the jet typically has a meandering shape, and these meanders themselves propagate eastward, at lower speeds than that of the actual wind within the flow.
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